Drawn strand filled tubing wire

ABSTRACT

A wire for use in medical applications. The wire is formed by forming a bundle from a plurality of drawn filled tubing strands and positioning the bundle within an outer tubing. The tubing and strands are then drawn down to a predetermined diameter to form a wire for use in the medical devices. The wire may be covered with an insulating material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drawn strand filled tubing wire foruse in medical applications and in particular to such wire where thereis a need to apply an electrical voltage to human tissue.

2. Description of the Related Art

Implantable devices used in the medical field for applying electricalvoltage are customarily meant to stay implanted for several years. Suchdevices are used as pacing leads, for example. These medical devicesmust possess several characteristics including electrical conductivity,corrosion resistance, and biocompatibility. The medical devicesgenerally need to be flexible for snaking through arteries, for example.

Drawn filled tubing wire is a type of wire that has been usedextensively in medical devices. This wire includes an outer shell thatis filled with an electrically conductive material. While the materialsused for the outer shell are strong, they tend to be susceptible tocorrosion when contacted by body tissues and fluids. Therefore, drawnfilled tubing wire for medical use is customarily coated with aninsulating material such as silicone to prevent contact with human bodytissue. Pacing leads for applying an electric potential to the heartusually comprise two or three drawn filled tubing wires. Such leads aredescribed in U.S. Pat. Nos. 5,716,391, 5,755,760, 5,796,044, and5,871,531. A portion of the wires in such leads is generally encasedwithin a biocompatible material such as platinum, tantalum filledplatinum, tantalum filled platinum-iridium, or the like to allow anelectrical voltage to be applied from the wire to the desired tissuearea. A problem with such biocompatible materials is that they haveinsufficient strength and have limited electrical conductivity, andtherefore must be combined with the wire.

Referring to FIGS. 1A and 1B, a prior art pacing lead is shown for usein medical applications. Implantable cardio defibrillator (ICD) 20 isused for sensing electrical activity in the heart and for delivering ashock if heart activity slows or stops. ICD 20 is implantable and hasflexible, elongated conductive lead 26 (FIG. 1B) with electricalconnector 22 extending from one end thereof to plug into control 24 forcontrolling ICD 20 and for providing the electrical supply. Control 24is implanted just beneath the skin, often in the chest or abdomen.

Lead 26 is constructed from two or three electrically conductive wires27 such as wires having an alloy exterior tube filled with highlyconductive silver, for example. Each wire 27 is substantially coveredwith insulating material 29. Lead 26 is then substantially covered withinsulating material 28. At two locations along lead 26, coils 30 arelocated which are made from a biocompatible material such as platinum,tantalum filled platinum, tantalum filled platinum-iridium, or the like.Coils 30 are secured to individual wires 27 of lead 26 by any suitableprocess including laser welding. The portion of wire 27 in contact withcoil 30 has insulating material 29 removed to allow for the weldingprocess. These coils 30 form the contacts which engage the heart tissueat specific locations to deliver an electrical voltage, when control 24senses the need to deliver such voltage.

The interface between insulating material 28 and coils 30 must behermetically sealed to prevent fluids from contacting wires 27 of lead26 and causing corrosion and possible eventual failure of the ICD.Problems exist in that the achieving a hermetic seal of a polymericmaterial and a metal is difficult and costly. The bond may besusceptible to corrosion and bodily fluid leaking into the area betweencoil 30 or insulating materials 28, and wires 27 of lead 26. Inaddition, the materials used to form coils 30 are very flexible and maybe easily damaged simply from handling the coils. The welding processbetween wires 27 of lead 26 and coils 30 is a further step in themanufacturing process which increases the cost of production of ICD 20.

In the medical device industry, leads are used to transmit an electricalvoltage from an electrical supply source to an area in a human body. Thelead interfaces with tissues in the body so that an electrical signalmay be introduced to a particular area of the body. Such leads may beimplanted in a patient at any location in the body where theelectrophysiology needs to be monitored and/or artificially altered.Specific applications may be implantable defibrillators or pacing leads.The leads may also be used for pain relief or pain suppression in theback or spine relating to diseases such as Parkinson's disease. The leadmay be further implanted in the stomach to subside hunger pains. Forpatients with neurological damage, the leads might be used to replacethe nerve and act to transmit electrical signals from one place toanother in the body. These devices are most certainly used in humanshowever, they are not limited to humans and may be adapted for use inanimals.

The devices are designed for long term implantation and must haveseveral properties including resistivity, corrosion resistance,radiopacity, reliability, stiffness, fatigue life, weldability, MRIcompatibility, and biocompatibility. Other characteristics of the deviceinclude a predetermined ultimate tensile strength, Young's modulus,level of inclusions, fracture toughness, and percent elongation. Inaddition, the types of materials used, the construction, and the cost ofmanufacturing the device are all factors.

It is therefore an object of the present invention to provide a pacinglead with improved wires which eliminate the need for conductive coils.

It is therefore a further object of the present invention to reduce therisk of corrosion of the pacing lead.

It is therefore another object of the present invention to improveconductivity and flexibility of the pacing lead.

SUMMARY OF THE INVENTION

The present invention provides a wire for use in accomplishing theobjects set out hereinabove. The wire includes a plurality of strands,wires, or elements of material which are arranged in a particularorientation and are twisted or braided into a bundle before beingpositioned within an outer tube. The strands are formed from any of aplurality of materials to define the mechanical and electricalcharacteristics of the device. Such characteristics include corrosionresistance, strength, electrical conductivity, radiopacity, reliability,stiffness, fatigue life, weldability, MRI compatibility,biocompatibility and the like. In addition, a hollow strand may be usedto allow for fluid transfer along the length of the device for use indrug delivery to the patient, for example. Alternatively, a fiber opticstrand could be included as well as electrically insulated strands. Thetubing and strands are then drawn to a predetermined diameter to form awire for use in medical devices. The wire may be covered with aninsulating material.

An advantage of the present invention is that by use of the presentinvention, the need for conductive coils in pacing leads is eliminated.

Another advantage of the present invention is that the risk forcorrosion of the wires used in pacing leads and the like issignificantly reduced.

Yet another advantage of the present invention is that by using a wirehaving a plurality of strands or elements within the outer tubing, thewire is more flexible and is less subject to mechanical failure due tofatigue than prior art wires.

Still another advantage is a wire with improved conductivity and lowerbattery consumption when used in pacing leads.

Yet still another advantage is a wire which is more comfortable to thepatient.

A yet further advantage is that the wire would be more reliable as, evenif one strand were to fail, there are numerous strands within the wirewhich would not fail, i.e., the strands have redundancy.

A yet another advantage of the wire is that it would provide designflexibility.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1A is a perspective view of a prior art implantable cardiodefibrillator using materials in accordance with the prior art.

FIG. 1B is a sectional view of FIG. 1A taken along line 1B-1B.

FIG. 2A is a perspective view of an implantable cardio defibrillatorusing a lead in accordance with the present invention.

FIG. 2B is a sectional view of FIG. 2A taken along line 2B-2B.

FIG. 3 is an exploded perspective view of a plurality of twisted strandsassembled within a tube.

FIG. 4 is a sectional view of the assembled plurality of twisted strandsand outer tube of FIG. 3.

FIG. 5 is a sectional view of the assembled plurality of strands andouter tubing of FIG. 4 after drawing of the assembly.

FIG. 6 is a sectional view of the assembled plurality of strands andouter tubing after drawing of the assembly to a smaller diameter thanthat shown in FIG. 5.

FIG. 7 is a sectional view of the assembled plurality of strands andouter tubing after drawing of the assembly to a smaller diameter thanthat shown in FIG. 6.

FIG. 8 is a sectional view of an alternative arrangement of a pluralityof strands.

FIG. 9 is a sectional view of the alternative arrangement of FIG. 8located in an outer tubing.

FIG. 10 is a sectional view of a third arrangement of a plurality ofstrands assembled with an outer tubing.

FIG. 11 is a sectional view of a fourth arrangement showing theplurality of strands assembled with an outer tubing FIG. 9 locatedwithin a second outer tubing.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates the invention, the embodiments disclosed below arenot intended to be exhaustive or to be construed as limiting the scopeof the invention to the precise forms disclosed.

DESCRIPTION OF THE PRESENT INVENTION

Referring to FIG. 2A, one example of a device utilizing the lead formedin accordance with the present invention is illustrated. Implantablecardio defibrillator (ICD) 32 includes an elongated lead used to shockthe heart when the heart rate becomes irregular. ICD 32 has first end 34and second end 36. First end 34 is provided with electrical connectors38 which engage control 40 which includes an electrical supply orbattery pack. Control 40 is implanted just beneath the skin of thepatient and is designed to have a long life so that frequent removal andreplacement is unnecessary. Second end 36 is mounted in the area of thebody being sensed which, in this example, is the heart. Second end 36 isprovided with barbs 42 which anchor the end of ICD 32 in place. Lead 43extends the length of ICD 32 and includes three wires 44. End 46 of onewire 44 has barbs 42 mounted thereon and is exposed. Wire end 46 acts asa sensor to monitor the heart's activity and initiate shock treatmentsto the heart when necessary.

Referring to FIGS. 2A and 2B, lead 43 is covered with a layer ofinsulating material 48 which may be formed from any suitable,biocompatible material such as, for example, urethane, to electricallyinsulate the conductor. Insulating material 48 substantially extends thelength of lead 43 with the exception of wire end 46 and contact sections50A and 50B. One wire 44 of lead 43 is exposed to the body tissues atend 46 and at each contact sections 50A and 50B so as to interface withthe body tissues and deliver an electrical shock as necessary. By usingthree wires to define three electrical contact points along lead 43,electrical potential is created between end 46, and contact sections 50Aand 50B. Contact sections 50A and 50B are spaced apart a predetermineddistance which coincides with the anatomy of the particular patient.

Referring now to FIGS. 3 and 4, wire 44 is constructed such that it actsas both the electrical contact surface and the electrical lead, thusmaking coils 30 of FIG. 1A unnecessary for providing the interfacebetween the conductor and the body tissue. Thus, corrosion at theurethane to metal joint of FIG. 1B between insulating material 28 andcoils 30 is eliminated. In addition, since fragile coils 30 are alsoeliminated, the cost of assembly and materials is reduced.

Wire 44 comprises drawn strand filled tubing wire formed from outertubing 52 and a plurality of strands, elements or wires 54. Each of thestrands may comprise a drawn filled tube wire. The initial size of thestrand diameter may be in the range of 1 mm-11 mm. The plurality ofstrands 54 are twisted or braided into a braided bundle as shown in FIG.3 with the outer strands being rotated about center strand 56. Thetwisted plurality of strands 54 is positioned within outer tubing 52 andthe conductor is thereafter drawn to the desired diameter. The twistingof strands 54 into a braided bundle ensures that wire 44 has the correctorientation of strands 54 throughout its length after being drawn. Aswire 44 is drawn, strands 54 are lengthened and align in thepredetermined arrangement. The diameter of drawn outer tubing 52 may bein the range of 2-12 mm, for example, but may be smaller for certainapplications.

There are several advantages to using strands 54 inside tubing 52.Strands 54 provide a more flexible wire 44 which is an important factorwhen snaking wire 44 through the patient's arteries, for example. Themore strands 54 used, the greater the flexibility. Additionally, overallfatigue life is improved for wire 44. For example, if one strand 54 hasa crack initiated at a high stress point or stress riser so strand 54ultimately fails, fatigue must be reinitiated in another of strands 54until all of strands 54 fail before wire 44 fails completely, thusimproving the life of wire 44.

Wire 44 is a metal-to-metal composite that combines the desired physicaland mechanical properties of two or more materials into a single lead.Wire 44 is drawn at ambient temperature. However, as the drawing processoccurs, the temperature and pressures increase significantly causing theformation of mechanical bonds between strands 54 and outer tubing 52. Byusing the drawn strand filled tube technology, dissimilar materials maybe combined to provide a variety of properties in a single conductor 54.The composite then has an outer tubing layer 52 which is biocompatibleand electrically conductive while the core material is designed toprovide strength, conductivity, radiopacity, resiliency, MRIenhancement, or the like.

In the embodiments shown in the figures, wire 44 is provided with 19strands 54. The number of strands 54 however may be any desired numberto fill tubing 52, or to provide particular properties to wire 44 aswill be discussed further hereinbelow. The diameter of the individualstrands 54 also determines the number of strands used to fill outertubing 52. In addition, the number of strands 54 directly relates to thecost of wire 44.

Outer tubing 52 is constructed from a biocompatible material so that thenecessary electrical contact is made directly between wire 44 and bodytissues. Such materials may include platinum or platinum alloys,tantalum or tantalum alloys, tantalum filled platinum, tantalum filledplatinum-iridium, or the like. Outer tubing 52 has a thickness which isdependent upon the type of wire 44 which is desired. The thicker thewall of outer tubing 52, the more rigidity it provides to wire 44. Ifthe wall of outer tubing 52 is made thinner, wire 44 is more flexibleand the cost of materials is reduced. The outer tubing however, shouldnot be made too thin so as to risk compromising the outer wall of wire44.

Referring to FIG. 4, a first embodiment of wire 44 is illustrated havingidentical strands 54. In this instance, strands 54 comprise drawn filledtubing wires. Stand 54 is a metal to metal composite comprising an outertubing 58 formed from any suitable material possessing thecharacteristics desired in wire 44. One such material may be acobalt-nickel-chromium alloy known as ASTM Standard F562. The ASTM F562material has characteristics including strength and long fatigue life.The strands 54 are filled with silver 60 because silver is ductile andmalleable, and has very high electrical and thermal conductivity. Oneacceptable type of strand is filled with 41 percent silver by weight.However, any suitable amount of silver or other suitable conductor maybe used. For example, if 60 percent silver, by weight, is used in thestrands, the strands have higher electrical and thermal conductivity.However, less ASTM F562 is then used and the strength of the strand isreduced. The combination of metals is ultimately determined by thedesired properties for each strand 64. An alternative material which maybe used in place of ASTM F562 material is a similar alloy. In additionto ASTM F562 materials such as ASTM Standard F90, F538, and othernickel, cobalt based super alloys, titanium, nitinol, and tantalummaterials may be used. A material which has a much longer fatigue lifethan ASTM F562 and which is described in U.S. Patent Application,entitled “Cobalt Nickel Chromium Molybdenum Alloy With A Reduced LevelOf Titanium Nitride Inclusions,” filed Sep. 5, 2003, the disclosure ofwhich is hereby incorporated herein by reference, may also be useful inparticular applications of lead 44.

Once the strands 54 are positioned within outer tubing 52, wire 44 isdrawn to reduce the diameter to the desired size. Referring to FIGS. 5,6, and 7, wire 44 is illustrated in stages as it is drawn to a smalldiameter. As the conductor is drawn, the strands 54 impinge upon oneanother and inner surface 62 of outer tubing 52. The round shape of eachstrand 54 is compromised by being compressed into adjacent strands 54and inner tubing surface 62. The material used for outer tubing 52 isrelatively ductile compared to ASTM F562, for example, which is whyinner tubing surface 62 becomes deformed as outer tubing 52 iscompressed against strands 54. The thickness of outer tubing 52 furtherdepends upon the ability of the tubing material to apply forces againststrands 54 to compress and deform the strands without compromising theouter tubing.

Referring to FIG. 7, center strand 56 has a substantially hexagonalcross section while the rest of strands 54 have non-hexagonal crosssections because they are in the transition area between the core andinner tubing surface 62. If the number of strands 54 is increased, thelayers of strands surrounding center stand 56 would increasingly show asubstantially hexagonal cross section, the hexagonal shape migratingfrom center strand 56 toward the outer transition layers.

In order to eliminate some of the deformation of inner tubing surface62, outer strands 54 could be swaged to develop facets which wouldengage surface 62. The interface between strands 54 and inner tubingsurface 62 may then be preserved due to the more uniform pressure beingexerted between strands 54 and outer tubing 52. This may help to reducethe risk of compromising a thinner walled outer tubing 52.

After wire 44 has been drawn to an appropriate length or cut from a rollof drawn strand filled tubing wire, for example, insulating material 49(FIG. 2B) is applied to the outer surface of outer tubing 52. Insulatingmaterial 49 is applied to each wire 44 in any suitable manner toelectrically insulate wires 44 and define the three contact points withthe body, sensor 46 and both contact sections 50A and 50B. Referring toFIG. 2B, a portion of insulating material 49 is removed from wire 44′ todefine contact section 50A with the other two wires 44″ and 44″′remaining completely insulated at contact section 50A. Similarly, aportion of insulting material 49 is removed from wire 44″ to definecontact section 50B. Insulating material 49 is removed at contact end 46of wire 44″′ to provide a sensor. The thickness of insulating material49 can be reduced since the sealing engagement between insulatingmaterial 28 and coils 30 of the prior art is eliminated. This sealingengagement is provided to prevent fluids from coming into contact withconductor 20 of the prior art. By completely encasing the inner,electrically conductive portion or strands 54 with a biocompatible outertubing 52, the risk of contact of fluids with strands 54 issubstantially eliminated. Thinner coatings of insulating material 49makes wires 44 and thus lead 43 more pliable, allowing for easierinsertion into a patient.

In addition, the manufacturing of wire 44 may be simplified by theelimination of coils 30. Insulating material 49 is simply removed fromwire 44 at sensor 46 and contact sections 50A and 50B to expose wire 44.Alternatively, sleeves of insulting material 49 may be positioned aboutthe outer surface of outer tubing 52 and drawn down with wire 44.

When constructing lead 43, insulating material 48 is then applied to thebundle of three wires 44′, 44″, and 44″′, by any suitable method so asto insulate and contain wires 44 while exposing the electrical contactareas sensor 46, and contact sections 50A and 50B. Insulating material48 also maintain the orientation of the wires, keeping the exposedportions of wires 44 aligned with the openings defining contact sections50A and 50B in insulating material 48.

Strands 54 located in outer tubing 52 may include various types ofmaterials to provide specific mechanical attributes to wire 44.Referring to the embodiment shown in FIGS. 8 and 9, several of strands54 are strands 64 as in the previous embodiment. The inner silver 60 ofstrands 64 provides electrical conductivity through wire 44 while outertubing 58 adds strength. To further strengthen wire 44 and improvefatigue life, solid strands 66 of materials including ASTM F562, and thelike may be included in the plurality of strands 54. Other propertiesmay be specifically addressed in wire 44 by adding different types ofstrands 54. For example, by adding solid platinum or tantalum strands68, radiopacity of wire 44 is enhanced. Tungsten has excellent corrosionresistance and may be added to improve that particular property of wire44. Ultimately, any types of strands 54 may be combined to create a lead44 have predetermined properties.

An alternative method of building the stiffness of wire 44 as shown inFIG. 11 would be to position strands 54 within a first tube of amaterial such as ASTM F562, for example, and then to position the ASTMF562 or strand filled tube wire in second, outer tubing 72 having theproperties required of outer tubing 52. Second tubing 72 would be of amaterial such as platinum, tantalum filled platinum, tantalum filledplatinum-iridium, or the like, all of which are biocompatible andelectrically conductive. The entire assembly could then be drawn to thedesired diameter. Further, second outer tubing 72 could be in the formof a strip which is wrapped around first tube 52 and laser welded.

Referring to FIG. 10, a further embodiment is illustrated in which oneof strands 54 is a tubular, hollow strand 70. Hollow strand 70 wouldallow for passage of fluid through wire 44 which may be useful forapplications involving drug delivery, for example.

Further, FIG. 11 also shows a DFT strand 64 which includes a silver core64, tubing 58, and an insulation layer 76. Additionally, FIG. 11 shows astrand 64 with a glass, fiber optic, core 78 and a metallic tubing 58.If desired, the tubing 58 could be deleted from core 78.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

1. A metallic wire comprising: an outer shell made of a first metal; anda plurality of wire elements disposed within said shell, each said wireelements comprising a metallic shell made of a second metal, saidmetallic shell filled with a third metal, said plurality of wireelements being compacted together whereby no voids exist within saidouter shell.
 2. The lead according to claim 1 wherein said first metalis biocompatible.
 3. The lead according to claim 1 wherein said firstmetal is platinum.
 4. The lead according to claim 1 wherein said thirdmetal is silver.
 5. The lead according to claim 1 wherein said secondmetal is ASTM Standard F562.
 6. The lead according to claim 1 whereinsaid wire elements are twisted together into a bundle.
 7. The leadaccording to claim 1 wherein said plurality of wire elements includes atleast one hollow tube.
 8. The lead according to claim 1 wherein at leasttwo of said plurality of metallic shells are filled with differentmetals.
 9. The lead according to claim 8 wherein one of said metallicshells is filled with silver and another of said metallic shells isfilled with tantalum.
 10. The lead according to claim 1 including alayer of electrically insulating material covering said outer shell. 11.The lead according to claim 1 including a second outer shell coveringsaid outer shell, said second outer shell made of a fourth metal.
 12. Amethod of making a lead, said method comprising: providing a first tubemade of a first metal, said first tube having a first diameter; forminga plurality of wire elements into a bundle, said wire elements eachcomprising a metallic shell made of a second metal, said metallic shellfilled with a third metal; inserting said bundle into said first tube toform an assembly; and thereafter drawing said assembly down to form awire with a second diameter.
 13. The method according to claim 12wherein said first metal is biocompatible.
 14. The method according toclaim 12 wherein at least two of said wire elements are filled withdifferent metals.
 15. The method according to claim 12 wherein saidthird metal is silver.
 16. The method according to claim 12 wherein saidfirst metal is platinum.
 17. The method according to claim 12 whereinsaid second metal is ASTM Standard F562.
 18. The method according toclaim 12 further comprising the step of, prior to said drawing step,providing a second metallic tube made of a fourth metal and insertingsaid assembly into said second metallic tube.
 19. The method accordingto claim 12 wherein said method further includes the step of coatingsaid first tube with an electrically non-conductive insulating material.20. A metallic wire comprising: an outer shell made of a first metal;and a plurality of wire elements disposed within said shell, at leastone said wire elements comprising a second metal, at least one said wireelements comprising a third metal, said plurality of wire elements beingcompacted together whereby no voids exist within said outer shell. 21.The wire according to claim 20 wherein one of said wire elements iscomprised of strands.
 22. The wire according to claim 21 wherein atleast one of said wire elements made of said second metal comprises atube and said tube is filled with a fourth metal.
 23. A method of makinga composite wire, said method comprising: providing a first tube made ofa first metal, said first tube having a first diameter; forming aplurality of wire elements into a bundle, at least one of said wireelements made of a second metal, at least one of said wire elements madeof a third metal; inserting said bundle into said first tube to form anassembly; and thereafter drawing said assembly down to form a wirehaving a second diameter.
 24. The method of claim 23 wherein one saidwire elements is comprised of strands.
 25. The wire according to claim23 wherein at least one of said wire elements comprises a tube made ofsaid second metal and said tube is filled with a fourth metal.